The present invention relates to an airbag device for protecting an occupant by deploying an airbag in a case of a vehicle collision. More particularly, the present invention relates to an airbag device that can quickly deploy an airbag into an adequate shape even with a low-output inflator.
Airbag devices, such as a driver-side airbag device, a passenger-side airbag device, a rear-side airbag device, and a side-protection airbag device, are used in order to protect the occupant in a case of emergency like a vehicle collision. Among various airbag devices, a whole structure of the passenger-side airbag device is stored in an instrument panel at a front of a vehicle cabin.
FIGS. 6(A) and 6(B) are schematic side views showing a manner of deployment in a conventional passenger-side airbag device. FIG. 6(A) shows a state during deployment, and FIG. 6(B) shows a state in which the passenger contacts the deployed airbag.
The airbag device shown in FIGS. 6(A) and 6(B) includes a retainer R placed in an upper part of an instrument panel IP of a vehicle so as to face a windshield W. A bag-shaped bag body B and an inflator I for supplying gas into the bag body B are stored in the retainer R. The bag body B is normally folded and stored in the retainer R.
A typical capacity of the deployed bag body B is 100 to 130 liters. A supply output of the inflator I is typically 400 to 550 kPa for a 60-liter tank.
The airbag device shown in FIGS. 6(A) and 6(B) operates as stated below. When the inflator I supplies the gas into the bag body B upon a vehicle collision, an upper part of the bag body B expands along the windshield W of the vehicle, and a lower part of the bag body B is deployed close to upper legs of a passenger PS, as shown in FIG. 6(A). The bag body B is completely deployed after a predetermined time, and the passenger PS that is moving forward because of inertia contacts the deployed bag body B, as shown in FIG. 6(B). After that, the bag body B absorbs the force of inertial of the passenger body.
In general, a passenger-side bag has a capacity larger than that of a driver-side bag (approximately double). Thus, an inflator for promptly deploying the passenger-side bag is required to have an output higher than that for the driver-side bag. However, if there is an obstacle just behind the instrument panel IP, an impact applied to the obstacle during the deployment becomes larger as the output of the inflator increases.
Accordingly, the output of the inflator of the airbag device may be simply reduced in order to minimize the impact. However, when only the inflator output is decreased without changing other structures of the airbag device, the following problem arises.
FIGS. 7(A) and 7(B) are schematic side views showing a manner of deployment of a passenger-side airbag in which the output of the inflator is intentionally decreased. FIG. 7(A) shows a state during deployment, and FIG. 7(B) shows a state in which the passenger advances toward the deployed airbag.
FIGS. 7(A) and 7(B) show an operation and problems with the inflator with a decreased output in the airbag device. Namely, upon a vehicle collision, an inflator Ixe2x80x2 supplies gas into a bag body B. In case the inflator output is decreased, even though the bag body B is deployed in a range from a head to a waist of the passenger PS, as shown in FIG. 7(A), it is not yet completely deployed by the time when the passenger PS advances thereto. For this reason, in the worst case, the force of inertial of the passenger PS may not be sufficiently absorbed, as shown in FIG. 7(B).
On the other hand, U.S. Pat. No. 3,642,303 discloses an airbag having a lower bag segment and an upper bag segment. In this airbag device, the bag is structured to have a head bag (an upper bag segment) placed on a torso bag (a lower bag segment) with an orifice therebetween. When the bag is inflated, a trunk of a passenger first contacts the torso bag, and the applied impact causes gas in the torso bag to flow into the head bag through the orifice. This enables to use the gas efficiently.
The present invention has been made in view of such a background, and an object of the invention is to provide an airbag device that can quickly deploy an airbag into an adequate shape even with a low-output inflator.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to overcome the above problems, an airbag device of the present invention includes an airbag that is deployed in front of a passenger""s seat of a car, and an inflator for injecting gas to deploy the airbag. The airbag includes a lower bag segment for holding shoulders and a chest of an adult passenger when it is deployed, an upper bag segment that rises from the lower bag segment so as to hold a head of the adult passenger when it is deployed, and a partition cloth having an inner vent hole for separating the lower and upper bag segments. The inflator supplies the gas directly to the lower bag segment, and then to the upper bag segment through the inner vent hole.
In the airbag device of the present invention, when the bag is deployed, the lower bag segment is first inflated so as to hold the shoulders and chest of the adult passenger and keep the passenger from advancing. Accordingly, the device can support an upper body of the passenger more effectively than that disclosed in U.S. Pat. No. 3,624,303 in which the lower bag segment contacts a middle part of the adult passenger. The gas supplied from the lower bag segment through the inner vent hole deploys the upper bag segment. When the passenger is pressed into the lower bag segment, a part of the gas in the lower bag segment is transferred to the upper bag segment. Due to this mechanism, it is possible to restrain the passenger more reliably than the conventional airbag device even when the inflator output is low.
In the airbag device of the present invention, it is preferable that a capacity of the deployed lower bag segment be 60 to 90 liters. In this case, the lower bag segment can be deployed at a high speed even with the low-output inflator due to the relatively small capacity of the lower bag segment.
In the airbag device of the present invention, it is preferable that the output of the inflator be 300 to 400 kPa for a 60-liter tank. In this case, as the output of the inflator is low, the impact on an obstacle caused by the bag deployment can be reduced.
In the airbag device of the present invention, it is preferable that the upper bag segment be shaped like a triangular prism pointing upward with a capacity of 20 to 40 liters when it is deployed. It is also preferable that a space be formed between a front side of the deployed bag and a windshield. In this case, the output of the inflator may be further decreased as the capacity of the upper bag segment becomes smaller.
In the airbag device of the present invention, a plurality of inner vent holes may be formed in a rear side of the partition cloth so as to be spaced from one another at left and right sides, and the upper bag segment may have a gas-discharging vent hole. In this case, since a gas-discharging path can be secured from the lower bag segment to the upper bag segment through the gas-discharging vent hole in a relatively early stage of the bag deployment, the impact on an obstacle caused by the deployment can be reduced.
In the airbag device of the present invention, it is preferable that a rear surface of the upper bag segment be disposed slightly offset from a rear surface of the lower bag segment toward a front side when the airbag is deployed. Consequently, a surface of the upper bag segment for receiving the head of the occupant is placed ahead of a surface of the lower bag segment for receiving the shoulders and chest of the occupant. In this case, the lower bag segment is first deployed so as to restrain the shoulders and chest of the passenger, and a portion to be squashed of the lower bag segment on the rear side of the upper bag segment starts to be squashed. The gas from the squashed portion flows into the upper bag segment through the inner vent hole, so that the upper bag segment is gradually deployed.
Since the rear surface of the upper bag segment is disposed slightly offset to the front side, when the upper bag segment is almost completely deployed, the head of the passenger is brought into contact with the upper bag segment, and is received by the soft upper bag segment. While the passenger is advancing, the lower bag segment is further squashed, and the gas continuously flows into the upper bag segment. A part of the gas, which is not necessary to restrain the head of the passenger, is discharged from the vent holes formed in the right and left sides of the upper bag segment. Consequently, the deployed upper bag segment remains soft and can softly restrain the head of the passenger.
In the airbag device of the present invention, the airbag may be folded so that a base portion is offset to the rear side, and other portions are folded like bellows in front of the base portion. In this case, when the airbag hits an obstacle during the deployment, a leading end of the bag can easily pass between the obstacle and the windshield. For this reason, the impact on the obstacle is reduced.
In the airbag device of the present invention, the lower bag segment of the airbag may have a gas-discharging vent hole at the base portion on the lower side thereof. The above-described folding manner makes it possible to preferentially deploy the airbag from a rear side of the base portion. In this case, since the gas is discharged out of the bag through the vent hole so as to reduce the impact due to the bag deployment when the bag is not deployed in a usual manner, it is possible to reduce the impact on the obstacle in a bag deploying direction caused by the bag deployment. In contrast, when the bag is normally deployed, the vent hole is covered as it contacts the upper surface of the instrument panel, and therefore, little gas is released.